Friction coupling

ABSTRACT

A friction coupling has a drive part, an output part, and a friction element which can transfer a friction moment between the drive part and the output part. A release element is provided which after a predetermined rotation angle of the friction coupling can act on the friction element so that a reduction of the friction moment occurs.

The invention relates to a friction coupling with a drive part, anoutput part and a friction element which can transfer a friction momentbetween the drive part and the output part. The invention relates inparticular to such a friction coupling which can be used in a vehicleoccupant restraint system.

BACKGROUND OF THE INVENTION

Friction couplings can be used in various ways in vehicle occupantrestraint systems. Examples of these are an arrangement for putting atrest for sensors, the drive of reversible belt tensioners, loop brakes,motion dampers in movable buckle extenders, rotation speed limiters inbelt locking systems or the like. All friction couplings have in commonhere the fact that a defined prestressing of the friction element, adefined looping angle and a particular friction factor are required. Thefriction moment provided by the friction coupling increasesexponentially with an increasing looping angle and increasing frictionvalue between the friction element and the component, on which thefriction element engages.

Owing to the exponential course of the friction moment, the minimumfriction moment transferred from the friction coupling can be adjustedcomparatively simply within desired tolerances. This is more problematicwith the maximum friction moment which can be transferred from thefriction coupling. Deviations of the looping force of the frictionmoment from a nominal value upwards have a very much stronger effect onthe friction moment than deviations downwards.

The object of the invention consists in further developing a frictioncoupling of the type initially mentioned to the effect that the frictionmoment transferred to a maximum from the friction coupling is limited.

BRIEF DESCRIPTION OF THE INVENTION

For this purpose, in accordance with the invention a release element isprovided, which acts on the friction element after a predeterminedrotation angle of the friction coupling so that a reduction of thefriction moment is brought about. The invention is based on the basicidea of allowing the friction moment generated by the friction elementto act at the start of the rotation moment transfer from drive part tooutput part in each case. Even if this friction moment is very muchhigher than is actually desired, this has a positive effect sooner onthe operation of the friction coupling; it is therefore guaranteed underall circumstances that firstly a moment of rotation is transferred fromdrive part to output part. Only after the friction coupling hasundertaken a predetermined rotation angle is the friction element actedupon via the release element, in order to delimit the friction momentwhich is able to be transferred at a maximum from the friction coupling.This ensures that in an operation phase of the friction coupling, afterthe predetermined rotation angle has been run through and a functionassociated with the corresponding rotation has been carried out, aprecisely defined maximum friction moment is not exceeded. This ensuresthat in this operation phase, in which in particular a slipping throughof the friction coupling occurs, no undesirably high friction moment isin action.

According to an embodiment of the invention, the release element is astop at which an arm of the friction element comes to abut after thepredetermined rotation angle has been run through. In this way, anopening force is exerted onto the friction element, which leads to areduction of the friction force of the friction element and hence to areduction of the friction moment transferred between the drive part andthe output part.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described below with the aid of a preferred embodimentwhich is illustrated in the enclosed drawings. In these:

FIG. 1 shows a diagrammatic exploded drawing of a belt retractor with afriction coupling;

FIG. 2 shows a section through the components of FIG. 1 in installedstate;

FIG. 3 shows a side view of a shifting coupling, used in a beltretractor, in an initial position;

FIG. 4 shows a side view of the shifting coupling in coupled state;

FIG. 5 shows a diagrammatic side view of a friction coupling, used inthe belt retractor of FIG. 1, in a first operating phase;

FIG. 6 shows the friction coupling in a second operating phase;

FIG. 7 shows an alternative development of the friction coupling in thefirst operating phase;

FIG. 8 shows the friction coupling of FIG. 7 in a second operatingphase; and

FIG. 9 shows a diagram of the friction moment transferred under variousoperating states from the friction coupling.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1 a belt retractor for a vehicle safety belt is shown in anexploded view, which has a frame 5, in which a belt spool 10 isrotatably mounted. Coupled with the belt spool so as to be secure withrespect to rotation is a belt spool drive part 12, which has outer teeth20. The outer teeth are part of a shifting coupling by means of which adrive moment can be transferred from a wheel 24 to the belt spool. Thewheel 24 is connected with an electromotor (not illustrated) (see forexample DE 201 15 316).

The wheel 24 has an insert part 24 a in which several pockets 25 areformed, in which a catch 26 is arranged respectively, on which arestoring spring 28 acts. Each catch is arranged together with itsrestoring spring in one of the pockets 25, and the insert part 24 a isarranged, for example arrested, on the wheel 24. The catches 26 are thenheld swivellably in the respective pocket.

Axially adjacent to the wheel 24, a coupling disc 34 is arranged, whichis provided with control tongues 36 which project through recesses inthe insert part 24 a into the wheel 24, so that they can cooperate withthe catches 26. The coupling disc 34, together with the wheel 24, theinsert part 24 a, the catches 26 and the outer teeth 20, forms ashifting coupling.

The coupling disc 34 is supported on the frame 5 by means of a frictioncoupling. The friction coupling has a friction element which isconstructed here as a friction spring 52. The friction spring 52 isarranged in a groove 50 which is formed on the side of the coupling disc34 facing away form the wheel 24. The internal diameter of the frictionspring 52 is smaller in the initial state than the external diameter ofthe groove 50, so that the friction spring 52 sits in the groove 50 witha certain pre-stressing. The friction spring 52 is constructed as anannular spring which has a bent arm 54 at one end which acts as aclosure arm and is supported on the frame 5 of the belt retractor so asto be secure with regard to rotation. For this purpose, a supportelement 55 is provided (see FIG. 5). The friction spring 52 has at itsother end a bent arm 56 which acts as an opening arm and can cooperatewith a release element 58 (see likewise FIG. 5), which is arranged onthe frame 5. The friction spring 52 forms together with the couplingdisc 34 and the support element 55 a friction coupling which makespossible a slipping through of the coupling disc 34 as soon as thefriction moment between the friction spring and the groove 50 of thecoupling disc 34 is overcome. Depending on the direction of rotation ofthe coupling disc 34, either the coupling disc 34 or the support element55 acts as drive part; the other of the two acts as output part.

The operation of the shifting coupling (see FIGS. 3 and 4) and of thefriction coupling (see FIGS. 5 and 6) is described below. In the initialposition of the shifting coupling (see FIG. 3), the catches 26 are heldback by the restoring springs 28 so that they are not in engagement withthe outer teeth 20 of the belt spool drive part 12. In this case, thebelt spool 10 can freely rotate and belt band can be withdrawn from thebelt spool.

If the wheel 24 is set in rotation by the electromotor (notillustrated), the catches are entrained. As the coupling disc 34 issecured by means of the friction spring 52, the catches 26 run onto thecontrol tongues 36, whereby they are guided into the outer teeth 20 (seeFIG. 4). Now the wheel 24 is coupled with the belt spool 10, so that theelectromotor (not illustrated) can drive the belt spool in the windingdirection of the safety belt, whereby a pre-tensioning is carried out.In so doing, the coupling disc 34 is entrained via the control tongues36 (see arrow P in FIG. 5), which is possible without difficulty,because of the friction coupling between the coupling disc and the frame5 of the belt retractor.

The friction coupling is set so that the friction moment exerted by thesupport element 55 via the closure arm 54 and the friction spring 52onto the coupling disc 34 is in every case so great that the catches ofthe shifting coupling can be guided in. To increase the minimum frictionmoment of the friction coupling, a spring 60 can be provided, which isarranged between the support element 55 and the closure arm 54 of thefriction spring 52 and pre-stresses the closure arm 54 in the directionof closure of the friction spring 52.

During the rotation of the coupling disc 34 in the direction of thearrow P, a differentiation is to be made between two different cases. Ina first case, the friction moment which is provided is higher than therequired minimum friction moment, but not greater than a permissiblemaximum friction moment. In this case, the coupling disc 34 rotatesinside the friction spring 52, which remains approximately stationary inits position shown in FIG. 5. In a second case, the friction momentprovided by the friction coupling is greater than a permissible maximumfriction moment (and hence, of course, also greater than the requiredminimum friction moment). In this state, the coupling disc 34, when itis rotated in the direction of the arrow P, entrains the friction spring52 in an anticlockwise direction, which is permitted by the spring 60.After a predetermined rotation angle, the opening arm 56 abuts onto therelease element 58, whereby the two arms 54, 56 of the friction spring52 are moved apart. Thereby, the looping force of the friction spring 52decreases and thereby also the friction moment provided by the frictioncoupling. In this way, it is reliably prevented that an undesirably highfriction moment is in action. In FIGS. 7 and 8, an alternativeembodiment is shown. This differs from the friction coupling shown inFIGS. 5 and 6 in that the spring 60 is integrated into the closure arm54. The closure arm 54 is in fact constructed with a bent end which iselastically flexible.

The path of the friction moment M, transferred from the frictioncoupling, over a rotation angle α is illustrated for various operatingstates with the aid of FIG. 9. “Min” designates the moment of rotationwhich is necessary for guiding in the catches. “N” designates the momentof rotation which is provided as a minimum by the friction coupling. “H”designates the moment of rotation which is provided as a maximum by thefriction coupling.

At the start of the rotation of the wheel 24, the moment necessary forguiding in the catches 26 acts in the friction coupling. As soon as thecatches are guided in (rotation angle 1), the acting moment of rotationincreases, because the coupling disc 34 now has to be entrained.Assuming that the friction coupling provides a comparatively lowfriction moment, the acting moment of rotation rises for example up tothe level N and remains at this level over the further rotation angle(Path 1). If, on the other hand, the friction coupling provides a highmoment of rotation, then starting from the complete guiding in of thecatches 26, the acting moment of rotation would rise to the level H andthen remain at this level over the further rotation angle. This would beundesirable and is prevented. Owing to the spring 60, the frictionspring 52 in fact co-rotates as soon as a force F0 acts on it. Thereby,the rise in the moment of rotation is limited and the friction spring 52can be rotated contrary to a rising moment of rotation; the increase inthis range (Path 2) is determined by the elastic rigidity of the spring60. At point 2 of the rotation of the friction coupling, the opening arm56 arrives in abutment against the release element 58, and at point 3the inherent elasticity of the opening arm 56 is “used up”, so that thefriction spring 52 is now opened. Therefore, the acting moment ofrotation remains over the further rotation angle at a level which liesconsiderably below the maximum friction moment H (Path 3).

The path of the friction moment of the friction coupling can be setthrough the construction of the spring 60 and also the positioning ofthe support element 55 and of the release element 58. It is alsopossible to arrange the support element 55 and/or the release element 58displaceably on the frame 5 of the belt retractor, so that for exampledifferent states can be connected in depending on external parameters.These states can be connected for example through a belt windingscanning, a control via a gear similar to a chid's safety mechanism, bythe linear adjustment of a vertical adjuster, by the movement of thebelt buckle, by a relative movement in a locking system between couplingdisc and retractor axis or a movement of an end fitting of the safetybelt. The adjustment of the support element and/or of the releaseelement can also be controlled actively via an a actor, for example aholding magnet, a lifting magnet, an electromotor or the like.

The friction coupling according to the invention was described here aspart of a reversible belt tensioner. However, a variety of otherpossibilities of application are conceivable. For example, the frictioncoupling can be used for putting the sensor at rest with limitation ofthe friction force. It is also possible to use the friction coupling aspart of a recoil brake of a belt retractor, which prevents an abruptbraking of the belt spool with a rapid belt band return (and therebytriggers a blocking of the belt spool) by braking of the belt spool inline with a specific objective. It is also possible to use the frictioncoupling for damping lock movements. It is also possible to use thefriction coupling for a damped deflection fitting on the verticaladjuster as a function of the deflection angle and of the position ofthe vertical adjuster. The friction coupling can also be used inreversible tensioning processes, the force level acting on the belt bandbeing kept by a loop spring and thereby a guiding in of the lockingsystem being prevented. A reduction of the belt band force can berealized here by means of a movement of the housing mounting without anintrusive release impulse. The friction coupling can also be used inlock extender systems to limit the elastic force in swivel movements.The friction coupling can also be used in locking systems in order tovary the elastic force for catch guiding depending on the movement ofrotation and hence to favourably influence the dynamics, restoringbehaviour, belt locking and de-rattling. For example, with a returnmovement a higher force can act on the inertia disc, in order to actuatea return unblocking by means of different force levels and hence toachieve a minimum return rotation angle.

1. A friction coupling with a drive part, an output part, and a frictionelement which can transfer a friction moment between said drive part andsaid output part, characterized in that a release element is providedwhich after a predetermined rotation angle of said friction coupling canact on said friction element so that a reduction of said friction momentoccurs.
 2. The friction coupling according to claim 1, characterized inthat said release element is a stop.
 3. The friction coupling accordingto claim 2, characterized in that said release element is adjustable. 4.The friction coupling according to claim 1, characterized in that saidfriction element is a friction spring.
 5. The friction couplingaccording to claim 4, characterized in that said friction spring is aloop spring.
 6. The friction coupling according to claim 4,characterized in that said friction spring is an annular spring.
 7. Thefriction coupling according to claim 4, characterized in that saidfriction spring has an opening arm which can come into abutment againstsaid release element.
 8. The friction coupling according to claim 4,characterized in that said friction spring has a closure arm which cancooperate with a support element.
 9. The friction coupling according toclaim 8, characterized in that said support element is adjustable. 10.The friction coupling according to claim 8, characterized in that aspring is arranged between said closure arm and said support element.11. The friction coupling according to claim 10, characterized in thatsaid spring is constructed as a separate component.
 12. The frictioncoupling according to claim 10, characterized in that said spring isformed by an extension of said opening arm.
 13. The friction couplingaccording to claim 1, characterized in that it is part of a system forsetting at rest a sensor of a belt retractor.
 14. The friction couplingaccording to claim 1, characterized in that it is part of a return brakeof a belt retractor.
 15. The friction coupling according to claim 1,characterized in that it is part of a locking system of a beltretractor.
 16. The friction coupling according to claim 1, characterizedin that it is part of a belt buckle.
 17. The friction coupling accordingto claim 1, characterized in that it is part of a safety belt deflectionfitting.
 18. The friction coupling according to claim 1, characterizedin that it is part of a reversible belt tensioner.
 19. The frictioncoupling according to claim 1, characterized in that it is part of abelt extender system.
 20. The friction coupling according to claim 1,characterized in that it is part of a belt buckle extender system.